Some airlines have been allowing BlackBerrys to be used as electronic boarding passes and soon.
Now there is news of the iPhone being used to board a plane. Blogger Gerald Buckley writes about how he was allowed to board an American Airlines flight from San Antonio to Dallas by having the gate agent scan the bar code of the ticket on a PDF displayed on his iPhone.
Don't think you can waltz quickly to the gate by flashing your iPhone, though. Buckley makes it clear that he showed TSA his paper boarding pass to get through security.